[In the U.S. House of Representatives] Districts represented by Democrats are, together, only slightly more than half white and nearly one quarter Hispanic. Republican districts are roughly three-quarters white, and only one in nine residents is Hispanic.From here.
To the extent that Representatives in Congress are responsive mostly to the voters who voted for them, rather than to the entire electorate, the racial disparity between their core constituencies is much greater.
A substantial majority of the people who voted for the average Democratic member of Congress are non-white, and a disproportionate share of the whites who voted for them are non-Christians or openly not heterosexual. An overwhelming majority of people who voted for the average Republican member of Congress are heterosexual non-Hispanic white Christians.
This profound ethnic discontinuity between people who vote for Republicans who get elected to office and people who vote for Democrats who get elected to office is a major factor driving the deep partisan divide in Congress today. The greater ethnicity diversity of the Democratic coalition also drives the fact that the Republicans have a smaller political tent than the Democrats.